High dynamic range (HDR), high precision image and video content is now widely available. For example, digital cameras providing 12- or 14-bit HDR images are available. The JPEG committee is in the process of developing a new coding standard called JPEG XT (ISO/IEC 18477), which aims to provide both HDR image coding and backwards compatibility with standard JPEG (Joint Photographic Experts Group, ISO/IEC 10918) compression.
HDR data may be encoded using a JPEG XT encoder, to encode the data into base image layer data and extension image layer data. The base image layer data may be LDR (low dynamic range, sometimes referred to as SDR or standard dynamic range) data accessible to legacy implementations so that the JPEG XT encoded image can be decoded using a standard JPEG decoder, which can decode the LDR or SDR data and ignore the extension image layer data. The extension image layer data may be used for reconstructing an HDR image. To decode the JPEG XT encoded image, it is necessary to transfer both the encoded base image layer data and extension image layer data to a JPEG XT decoder for decoding.
It is desirable to provide a more efficient encoding method, for example for encoding HDR images. For example, it is desirable to provide an encoding method with reduced data transfer requirements for transfer of data between an encoder and a decoder. It is similarly desirable to provide a more efficient decoding method.